Abstract

Cross-phase modulation (XPM) is commonly viewed as a nonlinear process that chirps a probe pulse and modifies its spectrum when an intense pump pulse overlaps with it. Here we present an alternative view of XPM in which the pump pulse creates a moving refractive-index boundary that splits the probe pulse into two parts with distinct optical spectra through temporal reflection and refraction inside a dispersive nonlinear medium. The probe even undergoes a temporal version of total internal reflection for sufficiently intense pump pulses, a phenomenon that can be exploited for making temporal waveguides. In this paper we investigate the practical conditions under which XPM can be exploited for temporal reflection and waveguiding. The width and shape of pump pulses as well as the nature of medium dispersion at the pump and probe wavelength (normal versus anomalous) play important roles. A super-Gaussian shape of pump pulses is particularly helpful because of its relatively sharp edges. When the pump wavelength lies in the anomalous-dispersion regime, the pump pulse can form a soliton,whose unique properties can be exploited to advantage. We also discuss a potential application of XPM-induced temporal waveguides for compensating timing jitter.

USDOE National Nuclear Security Administration (NNSA); Univ. of Rochester, NY (United States); New York State Energy Research and Development Authority (NYSERDA); National Science Foundation (NSF); New York State Energy Research and Development Authority

@article{osti_1423130,
title = {Cross-phase-modulation-induced temporal reflection and waveguiding of optical pulses},
author = {Plansinis, Brent W. and Donaldson, William R. and Agrawal, Govind P.},
abstractNote = {Cross-phase modulation (XPM) is commonly viewed as a nonlinear process that chirps a probe pulse and modifies its spectrum when an intense pump pulse overlaps with it. Here we present an alternative view of XPM in which the pump pulse creates a moving refractive-index boundary that splits the probe pulse into two parts with distinct optical spectra through temporal reflection and refraction inside a dispersive nonlinear medium. The probe even undergoes a temporal version of total internal reflection for sufficiently intense pump pulses, a phenomenon that can be exploited for making temporal waveguides. In this paper we investigate the practical conditions under which XPM can be exploited for temporal reflection and waveguiding. The width and shape of pump pulses as well as the nature of medium dispersion at the pump and probe wavelength (normal versus anomalous) play important roles. A super-Gaussian shape of pump pulses is particularly helpful because of its relatively sharp edges. When the pump wavelength lies in the anomalous-dispersion regime, the pump pulse can form a soliton,whose unique properties can be exploited to advantage. We also discuss a potential application of XPM-induced temporal waveguides for compensating timing jitter.},
doi = {10.1364/JOSAB.35.000436},
journal = {Journal of the Optical Society of America. Part B, Optical Physics},
number = 2,
volume = 35,
place = {United States},
year = {2018},
month = {1}
}

Figures / Tables:

Fig. 1: Temporal (left column) and spectral (right column) evolutions over a 3-km-long fiber for the probe [(a),(b)] and pump [(c),(d)] pulse. The pump pulse has a super-Gaussian shape and is propagating at the zerodispersion wavelength of the fiber. See text for other parameter values. The time axis is measuredmore » in a reference frame that is moving with the pump pulse such that t − T − z/vg1« less

Here we discuss, temporal total internal reflection (TIR), in analogy to the conventional TIR of an optical beam at a dielectric interface, is the total reflection of an optical pulse inside a dispersive medium at a temporal boundary across which the refractive index changes. A pair of such boundaries separated in time acts as the temporal analog of planar dielectric waveguides. We study the propagation of optical pulses inside such temporal waveguides, both analytically and numerically, and show that the waveguide supports a finite number of temporal modes. We also discuss how a single-mode temporal waveguide can be created inmore » practice. In contrast with the spatial case, the confinement can occur even when the central region has a lower refractive index.« less

We show numerically that the spectrum of an optical pulse splits into multiple, widely separated, spectral bands when it arrives at a temporal boundary across which refractive index changes suddenly. At the same time, the pulse breaks into several temporally separated pulses traveling at different speeds. The number of such pulses depends on the dispersive properties of the medium. We study the effect of second- and third-order dispersion in detail but also consider briefly the impact of other higher-order terms. As a result, a temporal waveguide formed with two temporal boundaries can reflect the temporally separated pulses again and again,more » increasing the number of pulses trapped within the temporal waveguide.« less

We proposed a novel new architecture for a mode-locked laser oscillator/amplifier system at 2050 nm that is designed to achieve 300 fs pulse widths at a repetition rate of 119 MHz with an average power of greater than 1 W. The system is designed for application to free-electron laser (FEL)-based light sources and for the recently demonstrated micro-fabricated Dielectric Laser Accelerators (DLAs). The laser design uses hybrid-integration to directly incorporate carrier phase envelope (CEP) stabilization in the femtosecond modelocked laser oscillator cavity. This design eliminates all mechanical adjustments or moving parts that are currently used in CEP systems and requiremore » periodic alignment using mechanical motion. Most of the large free-space optical components currently used in femtosecond laser systems are replaced with waveguide chips that implement all the optical functions required for long term stability in a small compact footprint. One of key design features of our technology is the ability to lock the laser modelocking repetition rate to an external clock frequency. The design will also implement Carrier Envelop Pulse stabilization (CEP) to control the phase drift of the carrier wave relative to the peak of the pulse due to phase jitter or drift of the laser cavity. These capabilities are critical for all of the anticipated DOE applications. A large design-of-experiments in a single chip having periodic and chirped gratings fabricated in silicon nitride and silica was assembled in an array of 450 waveguide variations supporting wavelengths from 780 nm to 2100 nm. A second wafer fabrication run was implemented after results from the first run showed that the lithography did not produce grating duty cycles and feature sizes as designed. This was corrected nearly perfectly in the second fabrication run, and the improvements were confirmed through microscopic and spectroscopic analysis. Using an optical vector analyzer, periodic gratings were characterized for insertion loss, reflectivity and transmission as a function of wavelength and grating geometry in order to identify the best design parameters for functional chirped gratings. In the process of analyzing the periodic gratings, a technique to derive very accurate values for the effective refractive index of the silicon nitride strip waveguides was developed. Also, an unexpected secondary scattering mechanism was observed. A detailed investigation of the secondary peak’s behavior led to the hypothesis that its appearance is a consequence of scattering from the components of the high contrast, segmented features of the third-order grating designs. This explanation is testable in subsequent wafer trials using the analysis methodology developed here by designing purely sinusoidal sidewall modulations along the waveguide that would suppress the scattering and reduce the Bragg reflection losses. Chirped gratings for wavelengths from 1550 nm to 2100 nm were investigated with the OVA for insertion loss and for chromatic dispersion as a function of wavelength and versus propagation distance. Negative and positive chirps ranging from 5 ps/nm to 80 ps/nm for 4 cm long gratings were characterized and confirmed as capable of providing stretching and compression factors of nearly 1000 for ultrashort pulses that are 300 fs wide with transform-limited 12 nm bandwidth. This performance is on-par with much larger and more complex free-space and fiber-based approaches. Compared to free-space or fiber pulse stretchers and compressors, this highly versatile material system and compact waveguide technology demonstrates considerable potential to meet or exceed the performance of conventional alternatives while reducing size, complexity and cost.« less

Here, we show numerically and analytically that temporal reflections from a moving refractive-index boundary act as an analog of Lloyd’s mirror, allowing a single pulse to produce interference fringes in time as it propagates inside a dispersive medium. This interference can be viewed as the pulse interfering with a virtual pulse that is identical to the first, except for a π-phase shift. Furthermore, if a second moving refractive-index boundary is added to create the analog of an optical waveguide, a single pulse can be self-imaged or made to produce two or more pulses by adjusting the propagation length in amore » process similar to the Talbot effect.« less

A time-to-frequency converter was constructed using an electro-optic phase modulator as a time lens, allowing the pulse shape in time to be transferred to the frequency domain. We used such a device to record the temporal shape of infrared pulses at a wavelength of 1053 nm (width about 7 ps) and compared these measurements to those made by using both a streak camera and an autocorrelator. This side-by-side comparison illustrates the benefits and limitations of each of the measurement methods. Numerical simulations were used to establish that our time-lens-based system can accurately measure the shape of infrared pulses between 3more » ps and 12 ps. We also use our numerical model to determine how such a system can be modified to measure pulses whose width lies in the range of 1–30 ps, a range of interest for the OMEGA-EP laser at the Laboratory for Laser Energetics.« less